There is no shortage of clip-on boards designed for the Raspberry Pi, almost all designed to make the tiny computer’s GPIO pins more accessible in order to ease the connection of devices to it, particularly ones that operate at voltages that are not Pi friendly.
Pimoroni/Cyntech Pibrella Jump to the beep: the Pibrella from …

This is, of course, how apps for modern operating systems are programmed: they do little or nothing until the user interacts with the UI, or data comes in from the network, say. But it’s not a common approach with embedded devices, such as Arduino.

Errrr... what is the writer of this smoking? Any vaguely sane (*) embedded developer spends their life with event driven code. Depending on the embedded system it will either have hardware support and masks for event triggers or for simpler systems the developer has to implement everything in an execution loop but it's still event driven. Or does the writer think that having events built into a high level language or API makes an application event driven?

* I've seen some complete balls-ups from developers who plainly had no idea what they were doing at a low level (and often at a high level either). It was usually quicker to rip everything up and start again than attempt to step through and debug a spaghetti mess of interwoven interface and state checking code. The basic flow usually never needed to be complicated, often something like this:

Connectivity?

There are a lot of 'nice' boards out there (still have not got round to checking them out yet). Most seem to 'capture' all of those 26 pins by not having a connector on the other side of the board that allows another board to be plugged in. A lot of Arduino shields do have this type of connector, so can be stacked. Still, it is cheap so I might check it out

Re: Connectivity?

There are stackable add-ons for the Pi as well. This solution is a bit of an abomination, but it looks like it can take any of the add-on cards so long as they don't have conflicting requirements for GPIO pins. This other supplier seems to have a saner approach, with single-purpose modules being stackable using I2C, I guess, so GPIO conflicts shouldn't happen provided everything has a unique I2C bus address.

Then, there's GrovePi (as mentioned in the latest MagPi, also this link) that does away with physical stacking and does everything through wiring up modules with a standard 4-wire connector. I think that's probably the neatest implementation for stuff like robots because you can route your sensors to where they make sense physically.

I think you were saying that in the Arduino world, it's quite common to have pass-through connectors for stacking. Using a Gertduino would let you build up a stack of such Arduino modules, with a Pi controlling the whole show on the bottom.

Re: Decent pass through connectors aren't cheap!

If you're building your own board, there's an Adafruit through connector on the Farnell website for £1.14 apiece. I think the Adafruit stuff tends to be pretty good quality, but I haven't used this particular item.

Re: Decent pass through connectors aren't cheap!

Great, but what I really want is a female-to-female version that'll drop onto the Pi's GPIO pins and give be Arduino-style connectors instead. Dunno if I'm using the wrong search terms, but I'm darned if I can find one of these.

These are great for primary school

My wife bought 3 of these for her primary school and the kids love them. I wrote a scripting language for it so the kids can do more with them than they could with ScratchGPIO. It's on github here: https://github.com/scott-vincent/pioscript